1. Field of the Invention
The present invention relates to an imaging device, and more particularly, to an imaging device provided with an autofocus function that automatically performs focus adjustment of an imaging device such as a digital camera or the like.
2. Description of the Related Art
In recent years digital cameras have been commonly used as imaging devices for photographing subjects. A conventional digital camera (such as a digital still camera or digital video camera) generally acquires an image by using an imaging element such as a CCD or the like, and records the image as digital image data in an internal memory or IC card provided inside the camera or on a recording medium such as a magnetic tape or the like. The image can then, on the basis of the recorded image data, be recorded onto recording paper by a printer. Also, the image acquired by imaging can be displayed on a monitor. Moreover, it is known that many of these digital cameras are provided with liquid crystal monitors. With a digital camera that is provided with a liquid crystal monitor, a photographed image can be directly displayed on the liquid crystal monitor.
In an imaging device such as the above-described digital camera, a lens is provided for the purpose of focusing a subject image onto the imaging element when a subject is being photographed. By controlling focusing of the lens, a focusing distance can be aligned with the subject. Consequently, imaging devices provided with autofocus functions for automatically aligning focusing distances with subjects have been conventionally suggested.
However, autofocus functions in conventional imaging devices perform focusing on the basis of contrast values calculated from density data that has been input from the imaging element (CCD or the like). Therefore, these autofocus functions work for usual photography but sometimes do not function properly for situations such as close-up shooting, shooting in low ambient light levels and the like.
Accordingly, a technique, described in Japanese Patent Application Laid-Open (JP-A) No. 8-160287, has been suggested in which an imaging device has a macro mode and a normal mode. A focusing lens is moved in a predetermined manner in accordance with switching of these modes. Then a photograph is taken.
Further, a technique described in JP-A Nos. 6-22259 and 9-179014 has been suggested. In this technique, focusing distance is not automatically adjusted by an autofocus function in low lightness conditions; that is, conditions in which adjusting the focusing distance is difficult. Rather, in such conditions the focusing distance is predeterminedly set to infinity (so-called preset focus).
However, conventional imaging devices have a problem with focus searches taking a long time. For example, if an in-focus position is a position far from a focus search start position, the autofocus function must search through almost the whole of a focus search range.
Moreover, in cases in which adjusting the focusing distance is difficult, the focusing distance is not automatically adjusted but is predeterminedly set to infinity. Therefore, in cases such as close-up shooting, shooting in low ambient light levels and the like, this predetermined infinity focus setting may not be reasonable, which is a problem.